According to an analysis to be released on Friday, the trade group reports having its slowest quarter since 2007, adding just 395 megawatts of wind power capacity.

For the year to date, new installations were down 72 percent.

The reasons are many.

For starters, as any number of unemployed Americans can testify, the nation’s economic engines just aren’t humming like they used to, and that means less demand for electricity overall. Natural gas, the chief fossil-fuel competitor to renewable sources of electricity, is also dirt cheap these days, making wind power a tougher sell for cost-conscious utilities and state regulators.

But the wind association — and advocates for increased renewable electricity capacity over all — argue that policy is a problem, too. Despite lots of talk on Capitol Hill about the hazards of fossil fuels, their contribution to climate change and the need for broad, long-term supports for the renewables industry, legislators have so far failed to reach agreement on what that might look like.

Absent such policies, they argue, investment is riskier, clean power deals are harder to broker, and entrenched fossil fuel sources like coal and natural gas enjoy an advantage.

“If federal policymakers do not act quickly to provide investment certainty through a Renewable Electricity Standard, and longer-term tax policy like our competitors enjoy,” Denise Bode, the chief executive of the wind association, said in a prepared statement, “the U.S. wind industry will continue to stall out.”

Elizabeth Salerno, director of industry data and analysis with the American Wind Energy Association, said in a phone call that state-level policies have helped.

Roughly 30 states have mandatory targets for diversifying their energy portfolios with more renewable power. “They’ve been doing a great job leading the effort to get renewables installed over the past decade,” Ms. Salerno said.

But when demand for power shrinks, she added, the amount of renewable generation required by state mandates gets proportionately smaller too. “It’s not as aggressive a driver as it normally is,” she said. “And in any case, 30 different programs in 30 different states does not amount to a national signal.”

On a more granular level, the trade group reported some interesting developments — including Oregon’s emergence as the leader in new wind installations for the third quarter, eclipsing Texas, which has long held the top slot.

The reason, the group suggests, is that Texas has hit a transmission wall and is now trying to sort out how to get its west Texas wind resources to the load centers in the center of the state.